Air Infultration

Inspect around windows and doors, periodically.

Use a good silicone caulk.  In many cases, you can pick up a tube of caulk and take care of small oversights faster than waiting for your builder?s warranty guys to get by to take care of a little job.

Doors should have weather stripping.  In most new construction, you?re going to have entry doors that have weatherstripping pre-attached at the factory, but it?s a good idea to check and make sure that it?s filling the gap at the bottom and around the rest of the door.

Check out your fireplace.  Make sure the damper is closed when you?re not burning wood in it, so you don?t have a lot of heated or air-conditioned air going right up your chimney ? those are energy dollars leaving your home!

Don?t underestimate the air that can leak through your wall switches and outlets either.  Very few builders are going to do this for you, but gaskets are easy to find that you can install yourself.  You may even want to plug in plastic inserts that a lot of people use for child protection.

Outside, look for cracks where two different types of building materials come together and also around windows and doors.  Gaps and cracks are also likely to occur wherever pipes, wires or TV cables penetrated the surface.

Fill cracks large than one-quarter inch with fiberglass, steel wool, or foam insulation and then caulk.

Sealing during construction.  All these measures will save you money every month on your utility bill, but if you?re around for the construction of your home, you can head off a huge amount of air infiltration problems by making sure the baseplate of your wall framing is sealed where it meets the foundation with a foam sealant during construction.

Air Infiltration Tests

Blower Door Test.  If you?ve checked all these things, and your house still feels drafty or you have unusually high heating and cooling bills, you might want to have a blower door test done.  Heating and air-conditioning professionals can set up and do the test in just a few minutes to let you know if your house has excessive leaks.

Infrared Test.  You can also have an infrared test done ? especially if you think your walls may be lacking insulation.  It?s a great way to pinpoint leaks, but it is pretty expensive.

Too Airtight?

Forced Air Intake.  A lot of homes are being built these days so airtight that getting enough fresh air in the home can become a concern.  Consult your builder or HVAC contractor about forced air intake systems.

Enough Air for Heaters.  If you have oil or wood burning heaters that draw air from inside the home to burn, making sure you have enough fresh air coming into the home is very important.

Open A Window.  If you just get the feeling once in a while that a room is getting too stuffy, you can open a window for a few minutes once or twice a day without causing a big loss of energy dollars, the way continuous air infiltration will.

All homes, through various connections to the outside, allow some amount of air leakage.  The air exchange rate is highly variable from house to house, and within a given house, depending on construction details, environmental forces (wind and air temperature), and the use of exhaust fans, dryers, etc.  Homes must have some minimum amount of air exchange in order provide oxygen for people and appliances, control humidity, eliminate odors, etc.  While some homes experience problems due to insufficient air exchange, most homes leak more than necessary most of the time.  Very few homes have the ability to truly control ventilation rates, which is only possible with a very tight house and some form of mechanical ventilation such as exhaust fans or heat recovery ventilators.

Older houses, in particular, tend to be very leaky.  While the rate of air leakage can vary greatly, it is not unusual for all the air in older homes to be replaced once each hour.  Recognized standards recommend a minimum air exchange rate of .35 (approximately 1/3) air changes per hour.  Very energy efficient houses are being built today with leakage rates as low as 0.05 natural air changes per hour, using controlled mechanical ventilation to ensure occupant health and comfort.

Benefits of Reducing Air Infiltration

Reducing air leakage from the house envelope and ductwork is typically among the most significant improvements that can be made to reduce energy use, as well as improve comfort, health, and building durability.  In winter, less cold, outdoor air would replace heated air, reducing drafts and cold areas.  In summer, more hot, humid air would be kept out of the house.  Pollen, dust, and radon entry can be reduced.  The potential for structural damage resulting from moisture being carried into walls or attics with leaking air would be decreased.  Another potential benefit associated with reducing air leakage, as with most other upgrades such as improved insulation or windows, is the ability to downsize heating and cooling equipment when it is replaced.

Factors to Consider

One factor to consider is the ultimate level of tightness desired.  With more extensive air sealing, some form of mechanical ventilation may become necessary.  A general rule is that exterior-vented bathroom and kitchen fans, equipped with timers, can provide adequate ventilation for homes with 0.20 to 0.35 natural air changes per hour.  Mechanical ventilation provides location-specific control of moisture and odors and lower energy use.  However, this approach is more expensive initially due to the additional time and material needed to tighten the house and the cost of any exhaust fans or heat recovery ventilators.

The present leakage rate of the house may also affect your decision to implement any air sealing.  Obviously, the more leaky a given house, the greater the potential benefits. 

Installation Issues

Ventilation - Ensuring adequate house ventilation is important.  A blower door can be used to determine if a particular house meets the standard(s) mentioned above for average air leakage/ventilation rates while also ensuring it is reasonably tight to minimize energy use.

Typical leak locations - Building air leakage typically occurs at several common locations.  Penetrations through the ceiling plane, for ducts, pipes, chimneys, etc., are common and are the most important holes to seal as they tend to be relatively large and the stack effect ("hot air rising") tends to drive air out of the top of the house.  For homes with naturally-drafted combustion appliances, air leakage from these holes may cause backdrafting.  Other typical leakage locations are around windows and doors, at the bottom of walls where they meet the floor, and the first floor/foundation wall joints.

Related Issues

Moisture - Moisture is produced by a number of sources including cooking, bathing, plant respiration, human activity, and combustion within the living space.  When a home is tightened, the average level of moisture (humidity) in the home almost always increases.  Controlling sources of moisture can be critical in a tight home to prevent condensation on windows, and within walls during cold weather.  Sources of excess moisture may be the result of any of the following:

Rainwater - check condition of roof, siding, caulking, gutters and downspouts, drainage of water away from home. 

Plumbing leaks. 

Cooking and Bathing - are there properly vented exhaust fans that can be used during, and up to 30 minutes after, cooking and bathing?

Clothes drying - is the dryer vented to the outdoors?

Venting/Drafting - Proper drafting of combustion appliances is an important health and safety issue.  Drafting patterns can be greatly affected by air sealing.  To verify proper drafting, tests can be performed which simulate worst-case house depressurization.  These tests generally involve turning on exhaust fans, opening and closing interior doors, and operating combustion appliances in various combinations to determine if and when backdrafting occurs.

Material Options And Testing

Reduction of leaks in a house involves sealing holes and cracks with a variety of materials including caulk, expanding foam, and sheet metal or other sheet materials (plywood, foam).  Densely installed insulation can also be effective in reducing air leakage through walls and ceilings.  In new construction, or retrofit where framing is exposed, polyethylene can be installed as an air and vapor barrier.  With proper installation, drywall and housewraps (such as Tyvek or Typar) can act as a good air (not vapor) barriers. 

Equipment is available that allows us to measure the leakiness of buildings and ductwork, as well as locate the source of leaks.  Called blower doors and duct blowers, these pieces of equipment pressurize or depressurize houses and duct systems, allowing measurement of air leakage and identification of specific leakage sites.

A number of other tests can also be performed using this and related equipment.  These include testing for proper flow of "return" air, proper operation of exhaust fans, and proper drafting of combustion appliances.  This last test is very important, as backdrafting of gas- and oil-fired furnaces, boilers, and water heaters can pose a serious health risk, and is more likely in tight houses.

These tests can usually be performed in 2-4 hours and are completely non-destructive.  Observing some of these tests can be very interesting and informative.  Therefore, it is strongly recommended that you be present to observe these tests if they are performed.

Existing Homes

Consider having air leakage testing performed early in a remodeling project.  The results of the tests may help you decide what approaches to take in regard to wall retrofit, window replacement, and duct improvements.  Decisions on the need for, and sizing of, new heating or cooling equipment may be affected by the results of leakage tests and any air sealing work subsequently performed.  If testing is performed by a contractor offering air sealing services, the air sealing can be performed at the same time as the testing.  Strongly consider having air leakage-related tests performed after sealing the house or ductwork, especially tests for proper drafting of combustion appliances.

New Construction

Compared to retrofit methods, reducing air leakage is much easier in new construction.  If you are adding any new rooms to the house, you should consider including some special air leakage detailing.  This detailing is easy to do and adds minimal first cost, while saving energy, increasing comfort, an extending the life of the house.

Sealing all horizontal and vertical construction joints, such as where two exterior walls meet or where a wall sits on a floor, should be considered standard practice.

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